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101.
Ping Cai Qiming He Xishi Wu Xuejian Liu Yan Liu Jie Yin Yihua Huang Zhengren Huang 《Ceramics International》2018,44(16):19135-19142
The W-doped Nb4AlC3 ceramics [(Nb1-xWx)4AlC3, x?=?0–0.0375] were successfully fabricated by in-situ reactive hot-press-aided method using elemental niobium, aluminum, graphite and tungsten powders. The XRD results suggest that the matrix phase (Nb1-xWx)4AlC3 and the second phase (Nb1-xWx)C were simultaneously formed when W was added. The SEM images show that (Nb1-xWx)C is dispersed in the W-doped Nb4AlC3 ceramics matrix. The mechanical properties of Nb4AlC3 were greatly enhanced by W doping. Typically, the (Nb0.975W0.025)4AlC3 exhibits the highest flexural strength (483?±?21?MPa), fracture toughness (8.5?±?0.3?MPa?m1/2) and Young′s modulus (382?±?18?GPa) at room temperature (RT), which are increased by 59%, 15% and 30%, respectively, compared with the present Nb4AlC3. The Vickers hardness of (Nb0.9625W0.0375)4AlC3 (4.8?±?0.2?GPa) is 92% higher than that of Nb4AlC3. The (Nb0.975W0.025)4AlC3 also retains a high flexural strength of 344?±?4?MPa at 1400?°C (71% of RT value), which is much higher than the RT flexural strength (303?±?22?MPa) of the present Nb4AlC3. The strengthening effect is attributed to the solid solution of W and the incorporation of the second phase (Nb1-xWx)C. The excellent mechanical properties endow the W-doped Nb4AlC3 ceramics as promising high-temperature structural materials. 相似文献
102.
Yong Li Sian Chen Haifeng Hu Chunrong Zou Zhihua Chen Xin Ma 《Ceramics International》2018,44(9):10175-10180
For process simplification and rapid densification of ceramic composites, a meltable single-source ZrC precursor was prepared by condensing zirconium acetylacetonate (Zr(acac)4) at 190?°C for 40–150?min. The preparation of ZrC precursor and the conversion from precursor to ceramics were investigated by using FTIR and NMR spectroscopies, GPC, DSC-TGA, XRD, SEM, EDS and TEM. The precursor had low viscosity (~ 10?mPa?s) and proper processing window (60?min) for precursor infiltration and pyrolysis (PIP). The ceramic yield at 1650?°C was 29.6%, and EDS revealed that the composition was (ZrC)0.337(HfC)0.0025(ZrO2)0.044C0.1865. The ceramics were composed of 0.2–0.5?µm grains which aggregated to form a stacked structure surrounded by amorphous carbon. The preparation processes were designed, and C/C-ZrC composites with the density of 2.45?g/cm3 were successfully fabricated through 11 cycles of PIP with Zr(acac)4. In conclusion, the synthetic method provides a simple and cheap route for precursors, and allows combined composite preparation with high efficiency. 相似文献
103.
Power Generation from Coke Oven Gas Using Chemical Looping Combustion: Thermodynamic Simulation 下载免费PDF全文
A chemical looping combustion (CLC) combined cycle with coke oven gas as fuel and NiO/NiAl2O4 as an oxygen carrier is proposed. The system was simulated by Aspen Plus® and the oxygen carrier circulation ratio was calculated. The effects of key operational temperatures and different gas turbines on the system performance were investigated. Under optimized conditions, a high CO2 capture efficiency could be achieved. To capture CO2 thoroughly, the PG6561B gas turbine can be employed, allowing for nearly 100 % CO2 capture efficiency. 相似文献
104.
Bingcheng Luo Xiaohui Wang Enke Tian Hongzhou Song Qiancheng Zhao Ziming Cai Wei Feng Longtu Li 《Journal of the European Ceramic Society》2018,38(4):1562-1568
Fe doped BaTiO3 ceramics with giant permittivity and low dielectric loss were synthesized in N2/H2 atmosphere started with BaTiO3 powders and iron powders. XRD analysis exhibited the tetragonal-pseudocubic phase transition when the Fe content is 3 mol%. XPS spectra confirmed the iron oxides with mixed-valence structure of Fe2+/Fe3+, while Ti-ions maintain Ti4+3d0 states without any oxidization-reduction. For the case of ceramics with 5 mol% Fe, the dielectric constant was 66,650 at 1000 Hz at room temperature, 19 times higher than that of pure BaTiO3 ceramics, while the dielectric loss tangent was 0.13. Comparison with other giant-permittivity materials demonstrated the superior potential of present ceramics. First-principles calculations investigated the interfacial interaction of Fe-[TiO2] interface and Fe-[BaO] interface. Giant dielectric constant was induced by the interfacial polarization between insulating ferroelectrics and semiconducting iron oxides with mixed-valence states, as well as the contribution from the generated electron hopping conduction. 相似文献
105.
完全匹配层边界条件存在两个问题,一是如何减少实际应用带来的额外存储量以及提升计算速度,另一个是如何提升匹配层的吸收效果。对于第一个问题发展了多种非分裂形式,本文采用一种直接对波场进行变换的新型非分裂方法,相比卷积完全匹配层具有不改变方程的形式以及易于实现等优势。对于如何进一步提升完全匹配层吸收效果,没有太大的进展。这是因为离散差异使匹配层的吸收问题更为复杂,一般采取增加匹配层层数的措施缩小离散差,但是又会导致计算量和存储量的增加。本文以在不增加匹配层层数以及不减小理论误差的情况下减小离散差异所带来的虚假反射为目的,分析传统的衰减因子,研究匹配层的吸收机理,设计新的衰减因子,以提高完全匹配层的吸收性能。新衰减因子能够进一步削弱虚假反射振幅,在匹配层层数为5~20层时,对应的边界反射振幅只有改进前的40%~80%。 相似文献
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109.
对热挤压的钛铜复合棒进行扩散处理,研究扩散退火温度及保温时间对界面结合强度的影响,并通过测试Ti和Cu在高温下的拉伸性能来选择较为合适的热轧温度。结果表明:扩散退火可有效促进界面处金属原子的扩散和增强结合强度,当扩散退火在780~800 ℃/30 min时复合界面的结合强度最高;钛铜复合棒热轧温度应选择780 ℃较为合适,此时Ti、Cu的强度和塑性指标相近,利于热轧时的均匀变形;钛铜复合棒的热轧结合机理可用N.Bay理论、热作用机制及位错学说进行解释。 相似文献
110.